Radiofrequency radiation

What's safe?

[The editorialist responds:]

Ronald Cridland questions the interpretation of health risk on the basis of radiofrequency exposure measurements and comparison to a permissible exposure guideline in the study by Thansandote and colleagues. [1] The results of risk assessment may change over time as additional studies become available. In addition, various assumptions must be made, such as the shape of the dose-response curve at low doses. Given these uncertainties it is difficult from a scientific perspective to deny risk definitively even at very low levels of exposure, especially when dealing with stochastic effects such as cancer.

The permissible exposure limits for radiofrequency radiation questioned by Cridland are based on the threshold for subtle thermal effects in tissue. [2] The specific absorption rate depends on frequency, and therefore the permissible exposure levels, measured in power density units, vary with frequency. The thermal effects associated with radiofrequency radiation demonstrate a clear threshold phenomenon. The very low levels of exposure to radiofrequency radiation measured in 5 Vancouver schools by Thansandote and colleagues [1] were orders of magnitude below the permissible limits and should not be associated with any thermal effects. The other health outcomes associated with radiofrequency - nonthermal effects and cancer - are at present speculative.

The interpretation of risk from ionizing radiation mentioned by Cridland is different because there is definitive evidence of risk of carcinogenicity for ionizing radiation and there are good data regarding dose response. Even if these currently speculative outcomes for radiofrequency radiation were later shown to be present, the risk would be dependent on absorbed dose and hence low in areas of measured low exposure of this ubiquitous form of non-ionizing radiation. Therefore, the results of the study by Thansandote and colleagues [1] should be reassuring after evaluation of the probability of any adverse health effects being associated with such exposure.